Before performing read DBI calibration, it is assumed that read DQ and write DQ calibrations have been completed.
The 0F0F0F0F pattern is written to the DRAM and
read back with read DBI enabled. The DRAM sends the data back as FFFFFFFF but the DBI pin has the clock pattern 01010101, that is used to measure the data valid window of the DBI input
pin itself. The final DQS location is determined based on the aggregate window for the
DQ and DBI pins.